[9front] patch: import replacement for ape/patch

[ori@eigenstate.org]

We've been dragging along an antique version of Gnu patch
as part of ape. It's a bulky program with built in remote
code execution as part of ed-style diffs.

I'd like to eventually kill it. Let's start
by adding a replacement:

diff 6fbb1acc8fa0b6655b14e8c46240a4a8d2d8c672 uncommitted
--- /dev/null
+++ b//sys/man/1/patch
@@ -1,0 +1,57 @@
+.TH PATCH 1
+.SH NAME
+patch \- apply diffs
+.SH SYNOPSIS
+.B patch
+[
+.B -R
+]
+[
+.B -p
+.I nstrip
+]
+[
+.B -f
+.I maxfuzz
+]
+[
+.B patch...
+]
+.SH DESCRIPTION
+.I Patch
+will take a patch file in unified diff format, and apply it,
+skipping leading and trailing junk.
+If the file is not an exact match, it will search forwards and
+backwards for the surrounding context up to
+.I maxfuzz
+lines.
+
+The following options are supported:
+.TP
+.I -R
+Reverse direction of the patch. Addtions become removals,
+and the new and old file names are swapped.
+.TP
+.I -p nstrip
+Remove
+.I nstrip
+elements from the paths to the files.
+.TP
+.I -f maxfuzz
+Controls how far
+.I patch
+searches for context when applying a patch.
+.SH SEE ALSO
+.IR diff (1)
+.IR git/export (1)
+
+.SH BUGS
+.PP
+The output of
+.IR diff -c
+is not handled
+.PP
+Reject files and backups are not supported
+.PP
+All files are processed in memory, which limits
+the files handled to 2 gigabytes.